An advantageous approach to fabricating assemblies including one or more light emitting diode (LED) die involves providing a thermally conductive base and mounting the one or more LED die on the base or within one or more cavities formed in an insulating layer overlying the metal base. The LED dice are thermally coupled to the metal base and heat from the dice is rapidly conducted through the metal base to one or more heat sinks. This approach may use as the thermally conductive base a substrate made using low temperature cofired ceramic-on-metal technology (LTCC-M), which is described in greater detail in U.S. Pat. No. 6,455,930 issued to Ponnuswamy et al. on Sep. 24, 2002 which is incorporated herein by reference. The resulting LED assemblies are particularly useful for high temperature operation. Alternatively, this approach may be used with any LED packaging technique that uses a thermally conductive base, such as metal base. According to an embodiment of the present invention, the base may be an LTCC-M substrate.
When using LTCC-M technology, mounting the LED die in close thermal coupling with the metal base is highly advantageous, but the die are peripherally circumscribed by ceramic cavity side walls. These side walls, unfortunately, absorb a significant amount of the light emitted from the LED die positioned within the cavity, thus reducing the amount of light emitted by the assembly.
One approach to increasing the light output is to attach a miniature metal reflector into each cavity of the ceramic-on-metal substrate. However this approach adds component costs (the reflector) and assembly costs (the depositing of adhesive, the placing of the reflector into the cavity and the curing of the adhesive). Accordingly there is a need for an improved method of increasing the light output of LED assemblies.